Re: [PATCH v4 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU

[Vladimir Murzin]

Ping again...

On 02/05/17 09:32, Vladimir Murzin wrote:
> Gentle ping!
> 
> On 24/04/17 11:16, Vladimir Murzin wrote:
>> It seem that addition of cache support for M-class CPUs uncovered
>> latent bug in DMA usage. NOMMU memory model has been treated as being
>> always consistent; however, for R/M CPU classes memory can be covered
>> by MPU which in turn might configure RAM as Normal i.e. bufferable and
>> cacheable. It breaks dma_alloc_coherent() and friends, since data can
>> stuck in caches now or be buffered.
>>
>> This patch set is trying to address the issue by providing region of
>> memory suitable for consistent DMA operations. It is supposed that
>> such region is marked by MPU as non-cacheable. Robin suggested to
>> advertise such memory as reserved shared-dma-pool, rather then using
>> homebrew command line option, and extend dma-coherent to provide
>> default DMA area in the similar way as it is done for CMA (PATCH
>> 4/7). It allows us to offload all bookkeeping on generic coherent DMA
>> framework, and it seems that it might be reused by other architectures
>> like c6x and blackfin.
>>
>> While reviewing/testing previous vesrions of the patch set it turned
>> out that dma-coherent does not take into account "dma-ranges" device
>> tree property, so it is addressed in PATCH 3/7.
>>
>> For ARM, dedicated DMA region is required for cases other than:
>>  - MMU/MPU is off
>>  - cpu is v7m w/o cache support
>>  - device is coherent
>>
>> In case one of the above conditions is true dma operations are forced
>> to be coherent and wired with dma_noop_ops.
>>
>> To make life easier NOMMU dma operations are kept in separate
>> compilation unit.
>>
>> Since the issue was reported in the same time as Benjamin sent his
>> patch [1] to allow mmap for NOMMU, his case is also addressed in this
>> series (PATCH 1/7 and PATCH 2/7).
>>
>> Thanks!
>>
>> [1] http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8633/1
>>
>> Cc: Joerg Roedel <jroedel@xxxxxxx>
>> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
>> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
>> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Rich Felker <dalias@xxxxxxxx>
>> Cc: Roger Quadros <rogerq@xxxxxx>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
>> Cc: Mark Rutland <mark.rutland@xxxxxxx>
>> Cc: Doug Ledford <dledford@xxxxxxxxxx>
>>
>> Changelog:
>> 	    v3 -> v4
>> 	       - rebased on v4.11-rc7
>> 	       - made CONFIG_ARM_DMA_MEM_BUFFERABLE optional for CPU_V7M
>> 	       - added Arnd's Acked-by
>>
>> 	    v2 -> v3
>> 	       - fixed warnings reported by Alexandre and kbuild robot
>>
>> 	    v1 -> v2
>> 	       - rebased on v4.11-rc1
>> 	       - added Robin's Reviewed-by
>> 	       - dedicated flag is introduced to use dev->dma_pfn_offset
>> 	         rather than mem->device_base in case memory region is
>> 		 configured via device tree (so Tested-by discarded there)
>>
>> 	RFC v6 -> v1
>> 	       - dropped RFC tag
>> 	       - added Alexandre's Tested-by
>>
>>
>> Vladimir Murzin (7):
>>   dma: Take into account dma_pfn_offset
>>   dma: Add simple dma_noop_mmap
>>   drivers: dma-coherent: Account dma_pfn_offset when used with device
>>     tree
>>   drivers: dma-coherent: Introduce default DMA pool
>>   ARM: NOMMU: Introduce dma operations for noMMU
>>   ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus
>>   ARM: dma-mapping: Remove traces of NOMMU code
>>
>>  .../bindings/reserved-memory/reserved-memory.txt   |   3 +
>>  arch/arm/Kconfig                                   |   1 +
>>  arch/arm/include/asm/dma-mapping.h                 |   2 +-
>>  arch/arm/mm/Kconfig                                |   4 +-
>>  arch/arm/mm/Makefile                               |   5 +-
>>  arch/arm/mm/dma-mapping-nommu.c                    | 253 +++++++++++++++++++++
>>  arch/arm/mm/dma-mapping.c                          |  29 +--
>>  drivers/base/dma-coherent.c                        |  74 +++++-
>>  lib/dma-noop.c                                     |  29 ++-
>>  9 files changed, 355 insertions(+), 45 deletions(-)
>>  create mode 100644 arch/arm/mm/dma-mapping-nommu.c
>>
> 
> 
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